1. Field of the Invention
The present invention generally relates to a brake retractor assembly for a motor vehicle. More specifically, it relates to a device that maintains a desired running clearance in the brake disks used in the brake assembly of an agricultural vehicle, such as a tractor.
2. Description of Related Technology
Brake assemblies are generally used to stop the movement of motor vehicles, such as an agricultural tractor. As shown in U.S. Pat. No. 6,002,976, the driveline of a typical agricultural tractor, for example a tractor in the John Deere 6000 series, includes an engine, a shifted multi-speed transmission, a reversing unit, a drive clutch, an optional creeper transmission, a shifted range transmission, and a rear axle differential gear which the drives the rear wheels. As shown in U.S. Pat. No. 5,197,574, a brake may also be provided between the transmission housing and the rear axle differential gear. Due to the low operating speeds, large mass and high torque under which agricultural tractors operate, these brakes are often configured so the brake disks are submerged in oil. The oil serves to lubricate and carry heat away from the brake disks when the brakes are applied by a tractor operator.
When the brakes are initially assembled, an optimal running clearance is set between a brake piston, the brake disks, separator plates (if applicable) and a brake cover. The optimal running clearance is carefully calibrated, depending on the geometry of a particular application, to minimize the response time and pedal throw required to engage the brake piston against the brake disks, while also minimizing the effects of windage (the frictional force acting on the oil caused by the relative motion of the brake disks to the brake piston separator plates and cover). Ideally, a very small running clearance is desired to allow for fast brake engagement and a short pedal throw. During brake disengagement, however, blowback (i.e., waviness, runout, or walking) of the brake disk can push the brake piston further away from the brake disk than desired, creating a larger running clearance than desired, and thus a longer pedal throw. This undesirably increases the brake pedal travel and response time required for brake engagement.
In view of the above, it is apparent that there exists a need for a brake retractor assembly for a motor vehicle that prevents blowback and maintains a desired running clearance of the brake disks.